1. Field of the Invention
The present invention relates to a method for forming images using a cylithographic imaging system. More particularly it relates to a method for forming images on plain paper and other non-reactive substances.
2. Description of the Prior Art
Photosensitive imaging systems employing microencapsulated radiation-sensitive compositions (also known as cylithographic imaging systems) are the subject of commonly assigned U.S. Pat. Nos. 4,399,209, 4,772,541 and 4,842,976 to The Mead Corporation. These imaging systems employ an imaging sheet including a layer of microcapsules containing a photosensitive composition in the internal phase. In the most typical embodiments, the photosensitive composition is a photopolymerizable composition including a polyethylenically unsaturated compound and a photoinitiator. Encapsulated with this composition is a color precursor. Exposure image-wise hardens the internal phase of the microcapsules. Following exposure, the imaging sheet is subjected to a uniform rupturing force by passing the sheet in contact with a developer sheet through the nip between a pair of pressure rollers whereupon the color precursor is transferred to the developer sheet where it reacts to form an image.
Techniques have been disclosed for forming images on plain paper. In U.S. Pat. No. 4,622,282 issued Nov. 11, 1986 a process is disclosed which comprises image-wise exposing an imaging sheet to actinic radiation. The imaging sheet includes a support having a layer of microcapsules containing a photosensitive composition and a color precursor on the surface. The sheet is subjected to a uniform rupturing force in contact with a sheet of plain paper. The chromogenic material is image-wise transferred to the sheet of plain paper to form a latent image and the surface of the sheet of plain paper carrying the latent image is then contacted with a developer material to form a visible image. In one embodiment a paper is contacted with a rotating developer applicator brush. The brush applies a developer material onto the surface of paper where it reacts with the chromogenic material and produces the color image. However, brush application of the developer is disadvantageous as it is often accompanied by streaking, loss of resolution and cross-colorization due to brush contamination, wherein the brush carries precursor and/or developer across the surface of the paper to undesired areas.
In accordance with another embodiment of the invention described in U.S. Pat. No. 4,622,282, the developer material is provided on the surface of the imaging sheet with the microcapsules containing the chromogenic material. The developer is provided in admixture with the microcapsules in a single layer on the surface of the imaging sheet or in a separate layer underlying the layer of microcapsules With the developer present on the surface of the imaging sheet, images are formed by simply image-wise exposing the sheet to actinic radiation, subjecting the sheet to a uniform rupturing force in contact with plain paper, and effecting transfer to the surface of the plain paper. The developer and the chromogenic material begin reacting as they are transferred to the surface of the plain paper.
U.S. Pat. No. 4,701,397 teaches another method for forming images on plain paper wherein a layer of microcapsules and developer is area-wise transferred to the surface of a plain sheet of paper to form an image. In this method, the microcapsules and developer are coated in a single layer or as separate layers on a thin polymeric film. The sheet is image-wise exposed to actinic radiation, assembled with a sheet of plain paper and subjected to pressure whereupon, in the image areas, the layer of developer is transferred (selectively adhered) to the paper and an image is formed.
U.K. Pat. Application No. 2 202 641 discloses a method for copying on paper or cloth using the cylithographic system wherein a wax is incorporated in the developer layer. The method relies upon two transfer steps. In the first, the image-wise exposed imaging sheet is assembled with a sheet of the developer on the surface of a temporary support, pressure is applied and a real image is formed on the developer sheet. The developer sheet is juxtaposed a sheet of paper and pressure is applied whereupon the developer layer is transferred to the paper surface.